As compared to one-dimensional codes, two-dimensional codes are capable of storing more information in a smaller area and are thus widely utilized in a variety of applications, such as inventory management and Web derivatives using mobile phones. Among two-dimensional codes, those whose size can be modified in accordance with the amount of data to be maintained therein are known. In the analysis of such a two-dimensional code, the size, direction and the like of the code are often unclear beforehand; therefore, this information are determined from a photographed image of the two-dimensional code.
A two-dimensional code comprises position detection patterns of a prescribed form for detecting the positional relationship of its photographed image. In such a two-dimensional code, the position detection patterns have a form that can be independently and easily distinguished from other parts. When a two-dimensional code is analyzed, on its photographed image, the position detection patterns are detected and conversion is performed based on their positional relationships. Detection of the position detection patterns is a fundamental process of the analysis and largely affects the recognition accuracy and the analysis time. Thus, the form of each position detection pattern is a critical element for two-dimensional codes.
As conventional two-dimensional codes, mainly the codes disclosed in Patent Literatures 1 and 2 are known.
Further, in two-dimensional codes, there is a need to recognize plural codes at the same time. As for the simultaneous recognition of plural codes, for example, when cardboard boxes each having a two-dimensional code pasted thereon are stored facing the same direction on a shelf and an inventory thereof is to be made, the work efficiency is improved if the two-dimensional codes could all be recognized at once from a distance, rather than recognizing the codes one by one at a short distance from each box. It is known that such simultaneous recognition can be done using an RFID or the like; however, RFIDs require an antenna or the like on the medium side, which leads to an increased medium cost. In contrast, two-dimensional codes are inexpensive because they can be used by simply printing them on a sheet of paper.